The present invention relates to an adaptive jitter canceller for cancelling phase jitter introduced into a transmission system.
In a prior art jitter canceller as shown and described in U.S. Pat. No. 4,639,939, issued to Hirosaki et al and assigned to the same assignee as the present invention, apparatus is described which extracts the carrier phase of a received QAM (quadrature amplitude modulation) signal and feeds it to a jitter prediction filter. The output of the prediction filter is used to compensate for the phase jitter. The jitter prediction filter is constructed of a finite impulse response (FIR) digital filter whose taps are adaptively controlled to affect the separation between noise components and phase jitter. However, a larger number of taps are required to ensure a high degree of accuracy. Typically, for a 128-QAM data modem with a baud rate of 2400 Hz, the number of taps would be in the range between 30 and 50. This requires a substantial amount of memory and calculation time.